The invention relates generally to wireless communications and, more particularly, to antenna reception diversity in wireless communications.
Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy, Communications Networks for Homes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10th century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network.
The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and a maximum asymmetric data transfer rate of 723 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a xe2x80x9cpiconet.xe2x80x9d Link management allows communication between piconets, thereby forming xe2x80x9cscatternets.xe2x80x9d Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices.
The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire 2.4 GHz ISM spectrum. Various error correcting schemes permit data packet protection by 1/3 and 2/3 rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput.
The Bluetooth protocol is specified in detail in Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference.
Fading is a well known problem in wireless communications systems such as Bluetooth systems. Antenna reception diversity techniques are conventionally used to overcome fading in wireless communications. With antenna reception diversity, a communication signal is received by a plurality of antennas, and the associated antenna signals are then suitably combined to produce the desired communication signal for the receiver. Antenna reception diversity techniques can therefore improve communication quality in the presence of fading.
It is therefore desirable to provide for improved antenna reception diversity in wireless communications systems such as Bluetooth systems.
The present invention provides antenna reception diversity wherein the received signal can be produced by combining the antenna signals with their associated fading amplitudes as estimated by a linear receiver. Also according to the invention, the antenna signals can be combined with their associated correlation values in place of estimated fading amplitudes. Further according to the invention, inherent characteristics of the receiver can be exploited such that the received signal is produced without any additional overhead that would otherwise be needed to provide estimated fading amplitudes.